1. Field of the Invention
The invention relates generally to the field of cancer chemotherapy and particularly to biologically active calcidiol derivatives for cancer cell inhibition.
2. Description of Background Art
Cancer is the second most common disease and also one of the most feared. Cancer occurs when cells continue to divide and fail to die at the appropriate time. Under normal circumstances, cells grow and divide to produce more cells as needed in order to maintain a healthy body. Tumors may form when this orderly process is disrupted by changes in regulatory processes that control normal cell growth and death, resulting in uncontrolled cell growth. Cancer may be induced by genetic changes, external factors such as diet, exposure to ultraviolet or other types of ionizing radiation, viruses, exposure to chemical carcinogens. In some cases, inherited genetic alterations may be a factor in development of cancer.
Regardless of which particular combination of factors contribute to the root cause of cancer, cumulative mutations may cause cancer cells to proliferate more rapidly than neighboring normal cells. Cell abnormalities passed down to cellular descendants may develop into clonal armies that continue to grow unabated. The cells may eventually develop the capacity through additional mutations to invade and destroy surrounding tissue. Thus, malignant cancers usually become life-threatening because they develop the power to disable the regulatory mechanisms that confine them to the specific tissue in which they arise. They subsequently disengage from the malignant tumor and travel through the bloodstream or lymphatic system where they eventually interfere with vital systems.
Novel therapeutic agents inhibiting tumor growth either directly or by impacting the tumor microenvironment are being developed and tested (Gershell L J, Atkins J H. A brief history of novel drug discovery technologies. Nat Rev Drug Discov. 2003; 2:321-327.) They include new classes of cytotoxic agents stimulating apoptosis, inhibiting angiogenesis and metastasis or alter tumor cell signaling pathways (Reed J C. Apoptosis-based therapies. Nat Rev Drug Discov. 2002; 1:111-121.) These new agents suppress tumor growth through multiple mechanisms. While core scaffolds have been used successfully in the past, (Tan D S. Current Progress in Natural Product-like Libraries for Discovery Screening Combinatorial Chemistry & High Throughput Screening, 2004; 7: 631-643) new compounds are necessary to advance the drug development efforts.
Neuroblastoma is a solid cancerous tumor that begins in nerve tissue in the /neck, chest, abdomen or pelvis but usually originates in the abdomen in adrenal gland tissue. By the time it is diagnosed, the cancer has usually metastasized to the lymph nodes, liver, lungs, bones and bone marrow.
Neuroblastoma (NB) is the most common heterogeneous and malignant tumor of early childhood. Two thirds of children with neuroblastoma are diagnosed when they are younger than 5 years. While frequently present at birth, neuroblastoma is usually not detected until later. In rare cases, neuroblastoma can be detected before birth by fetal ultrasound.
NB is the most common extracranial solid tumor in children. It is derived from the neural crest and is characterized by a marked clinical heterogeneity (aggressive, unremitting growth to spontaneous remission). Current treatment for high-risk patients includes surgery and high dose chemotherapy with autologous stem cell rescue. However, in spite of aggressive therapy, the disease relapses and up to 80% of patients die of disseminated disease. Eradication of refractory microscopic disease remains one of the most significant challenges in the treatment of high-risk neuroblastoma.
In a manner similar to other tumors, NB is known to produce endothelial growth factors that promote angiogenesis. Angiogenesis, the development of new blood vessels from the existing vasculature, is an essential component of solid tumor growth and metastasis. Several angiogenic factors are expressed by many tumors, suggesting that tumors promote their own vascularization by activating the host endothelium. Therefore, targeting angiogenesis is an attractive goal for targeting a variety of solid tumors including NB.
Treatment options for NB depend on age at diagnosis, tumor location, stage of the disease, regional lymph node involvement and the tumor biology. Generally four types of treatment are involved, alone or in combination, and include surgery to remove the tumor, radiation therapy, chemotherapy and bone marrow transplantation.
New and effective cancer treatments are constantly being sought. The most common therapies include radiation and drug treatments; unfortunately many are toxic and harmful to normal cells. Even when the majority of cells within a tumor are killed, a small number of unaffected cells may be able to reestablish the aberrant pattern of proliferation.
While most malignant cells appear at least initially to be highly susceptible to current cancer treatments, there is some speculation that subsets of cells are more resistant to drugs and radiation than normal, non-cancerous cells. Alternatively, tumor cells may simply develop resistance to chemical and radiation treatments, leading to recurrence of chemo- and/or radio-resistant cancers because the resistant cells maintain their ability to proliferate indefinitely. Resistance may also develop because administration of chemotherapeutic agents for the treatment of tumors is restricted by the toxicity of these agents to normal cells.
Deficiencies in the Art.
The severity of neuroblastoma is particularly disturbing. NB tumors grow aggressively, metastasize, induce angiogenesis and remain resistant to multimodal therapy, demonstrating the need for development of novel therapeutic strategies that address efficient inhibition of cancer cells and eradication of any remaining refractory microscopic disease.
There is an urgent need to improve the outcome for patients with this disease, with an increased emphasis for development of new drugs that are highly effective in eliminating aggressive cancer cells while also having insignificant toxicity toward normal cells.
Although state-of-the-art chemotherapy regimens have been established, the survival benefits still remain negligible (Saijo N, Tamura T, Nishio K. Strategy for the development of novel anticancer drugs. Cancer Chemother Pharmacol. 2003; 52 Suppl 1:S97-101). Therefore, effective new agents and innovative treatments are essential to fulfill this need. Intense and systematic research employing design and development of novel compounds along with in vitro and in vivo preclinical studies lead to the discovery of tumor specific agents that are useful as chemotherapeutic drugs. These novel agents may also lead to the identification of new molecular targets in cancer cells that can be furthered for drug development. Such discoveries create new frontiers for innovative cancer prevention and treatment strategies.